A class of industrial problems exists in which a large number of items must be separated, identified, counted and sorted. One example is the textile service industry, wherein soiled garments or linens are returned in large unsorted groups for cleaning and sorting. Present day means for solving this problem cover a broad spectrum. One solution uses manual workers who sequentially sort amongst the many items, picking single items manually and identifying the items visually. This solution is unsatisfactory because it is both slow and expensive, due to the high reliance on manual labor.
There are also numerous coding and sorting applications in the multi-billion dollar textile services industry whose requirements are not efficiently met by bar codes or radio frequency identification (RFID). A particularly challenging problem is the sorting of flat goods such as napkins, tablecloths, towels and bed linen items. These items, which range in size from very small to large, are presented in distorted orientations and undergo severe washing and ironing cycles. These are just some of the technology barriers to accurate machine identification and automated counting and sorting of flat goods and bulk garments. The lack of a viable coding and sorting solution for this segment of the textile services industry has resulted in high labor costs, lack of stock control, and reduced profits.
Thus, a technique that provides for the machine readable marking of rental textiles is important for inventory control at commercial laundries and other installations where large quantities of similar-looking materials must be handled in a high speed manner. Currently, only a small fraction of the rental textile industry uses machine readable coding. Most coding currently used to uniquely identify a rental textile item is simply text printed on a heat-sealed label attached to the item, and requires the presence of a human operator.
There are several reasons why the textile rental industry has only slowly adopted machine readable identification technology. Historically, the only available machine readable marking schemes for textiles were bar-codes and radio-frequency ID (RFID). Bar codes are the most commonly available type of machine readable marking in use today. However, tests of identification systems in actual laundries have shown that bar coding is not a robust coding technology on textile items. Bar codes are highly susceptible to degradation through both soiling and wear. Furthermore, due to the precise spatial information required for a bar code (line width and spacing), any warping of the label (almost assured on a fabric substrate) can result in high reading error rates. Finally, bar codes require line-of-sight and (generally) a specific orientation with respect to the detector, both of which are difficult conditions to satisfy under typical large scale laundry conditions.
In contrast, the radio-frequency ID technique does not suffer from the line of sight and soiling problems associated with bar codes. However, RFID remains expensive, both from initial cost and associated maintenance costs, and therefore is normally not economical for the rental textile industry. Furthermore, RFID tags have a tendency to exhibit cross-talk when they are in proximity to one another, which can preclude their use on closely-spaced sorting conveyors.
It can be appreciated that a need exists for a technology that has the ease of use and the low cost associated with bar codes, and yet is more robust and tolerant of the conditions found in large scale commercial laundries and other similar environments, such as large scale document and package handling facilities.
In U.S. Pat. No. 5,881,886 "Optically-Based Methods and Apparatus for Sorting Garments and Other Textiles" one of the inventors of this patent application has described various methods and apparatus that also address the problems referred to above.